U.S. patent application number 15/486640 was filed with the patent office on 2018-10-18 for solar panel power point tracker integrated with vehicle electrical system.
The applicant listed for this patent is Ford Global Technologies, LLC. Invention is credited to Daniel Boston, James A. Lathrop, Hadi Malek, Jacob Mathews.
Application Number | 20180297476 15/486640 |
Document ID | / |
Family ID | 62202746 |
Filed Date | 2018-10-18 |
United States Patent
Application |
20180297476 |
Kind Code |
A1 |
Malek; Hadi ; et
al. |
October 18, 2018 |
SOLAR PANEL POWER POINT TRACKER INTEGRATED WITH VEHICLE ELECTRICAL
SYSTEM
Abstract
A voltage quality module (VQM) function and a solar power
generation function are integrated by sharing a single voltage
converter (VC) within the electrical system of an automotive
vehicle with an electric-start internal combustion engine. The cost
of adding solar power generating capabilities to vehicles, the
packaging complexities of the systems, and the number of added
components are all decreased. The VC can be a DC-DC converter in a
boost mode or a buck mode. A switching circuit selectably couples
the VC between a main battery and an accessory bus or to between a
solar panel and an auxiliary battery. A VC controller regulating a
VC output using the main battery to stabilize an accessory bus
voltage when in an engine crank mode and otherwise regulating the
VC output to match an auxiliary battery voltage using the solar
panel output.
Inventors: |
Malek; Hadi; (Dearborn,
MI) ; Boston; Daniel; (Dearborn, MI) ;
Mathews; Jacob; (Canton, MI) ; Lathrop; James A.;
(Saline, MI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Ford Global Technologies, LLC |
Dearborn |
MI |
US |
|
|
Family ID: |
62202746 |
Appl. No.: |
15/486640 |
Filed: |
April 13, 2017 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B60L 50/16 20190201;
Y02E 10/50 20130101; B60L 2210/14 20130101; H02J 7/0068 20130101;
Y02T 90/12 20130101; Y02T 10/7072 20130101; Y02T 10/72 20130101;
H02J 7/35 20130101; B60L 2210/42 20130101; H02J 2310/48 20200101;
B60L 2210/12 20130101; G05F 1/67 20130101; B60L 1/003 20130101;
B60L 8/003 20130101 |
International
Class: |
B60L 8/00 20060101
B60L008/00; H02J 3/38 20060101 H02J003/38; H02J 7/35 20060101
H02J007/35; H02M 3/04 20060101 H02M003/04; H02M 7/44 20060101
H02M007/44 |
Claims
1. Apparatus for a vehicle with an electric-start internal
combustion engine, comprising: a DC accessory bus configured to
connect to a plurality of electrical accessories; a primary DC bus
adapted to connect to a main DC battery and to an electric starter
for the engine; a voltage quality unit including a voltage
converter configured to convert a voltage on the primary DC bus to
a stabilized voltage on the DC accessory bus during a starting
operation of the electric starter, wherein the voltage quality unit
includes bypass switches for connecting the primary DC bus to the
DC accessory bus when the electric starter is not in the starting
operation; and a solar panel generating an output voltage at a
panel output; wherein the bypass switches further connect the
voltage converter between the panel output and an auxiliary load
when the electric starter is not in the starting operation, and
wherein the voltage converter converts the solar panel output
voltage to an optimized voltage that optimizes power transfer to
the auxiliary load.
2. The apparatus of claim 1 wherein the stabilized voltage is a
predetermined nominal voltage of the main DC battery.
3. The apparatus of claim 1 wherein the voltage converter is a
boost converter.
4. The apparatus of claim 1 wherein the auxiliary load is comprised
of an auxiliary battery that is charged by the solar panel, and
wherein the optimized voltage is a predetermined nominal voltage of
the auxiliary battery.
5. The apparatus of claim 1 wherein the auxiliary load is comprised
of at least one DC load.
6. The apparatus of claim 5 wherein the DC load includes a DC-AC
inverter providing AC power to an AC load.
7. The apparatus of claim 1 further comprising a controller
configured to a) detect the starting operation, b) set the bypass
switches via at least one magnetic relay, and c) control a duty
cycle of the voltage converter to regulate the stabilized voltage
and the optimized voltage, respectively.
8. The apparatus of claim 1 further comprising a flow reversal
switch interconnecting the solar panel, voltage converter, and
auxiliary load to select either a boost mode or a buck mode of the
voltage converter as necessary to produce the optimized
voltage.
9. An automotive electrical system, comprising: a DC-DC converter;
a switching circuit selectably coupling the converter between a
main battery and an accessory bus during an engine crank mode or
otherwise between a solar panel and an auxiliary battery; and a
controller regulating a converter output using the main battery to
stabilize an accessory bus voltage during crank mode and otherwise
using the solar panel to match a voltage of the auxiliary
battery.
10. The system of claim 9 wherein the accessory bus voltage is
stabilized at a predetermined nominal voltage of the main
battery.
11. The system of claim 9 wherein the converter is a boost
converter.
12. The system of claim 9 the controller is configured to a) detect
the engine crank mode, b) set the switching circuit via at least
one magnetic relay, and c) control a duty cycle of the converter to
regulate the accessory bus voltage and the matching voltage,
respectively.
13. The system of claim 9 further comprising a flow reversal switch
interconnecting the solar panel, converter, and auxiliary battery
to select either a boost mode or a buck mode of the converter as
necessary to produce the matching voltage.
14. A control method for a voltage converter (VC) in a combustion
vehicle, comprising: converting solar power from a solar panel to
an optimized voltage for charging an auxiliary battery; detecting
cranking of a starter in the vehicle; during cranking,
disconnecting the VC from the solar panel and converting a main
battery power to a predetermined bus voltage for powering
electrical accessories; and after cranking, reconnecting the VC to
the solar panel and auxiliary battery.
15. The method of claim 14 wherein during cranking the VC is
connected to provide a power flow in a first direction through the
VC, and wherein the VC is connected to provide a power flow in an
opposite direction through the VC during conversion of solar
power.
16. The method of claim 14 wherein an input of the VC is switched
to the main battery during cranking and switched to the solar panel
otherwise.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] Not Applicable.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH
[0002] Not Applicable.
BACKGROUND OF THE INVENTION
[0003] The present invention relates in general to electrical
systems for motor vehicles equipped with solar panels for
generating electricity, and, more specifically, to variable voltage
converters for such systems.
[0004] Power generation using solar panels (e.g., photovoltaic
arrays) has received increasing attention in the automotive
industry due to their dropping price and improved efficiency levels
now available. Solar panels can be attached to a vehicle roof or
can be used to replace a moon-roof or sun-roof, for example.
Electricity generated by the panels can be used to charge an
onboard battery (such as an auxiliary battery, an electric
vehicle's high voltage battery, or the main 12V battery of a
gasoline-powered vehicle). A charge controller (e.g., a Maximum
Power Point Tracking, or MPPT, controller) is used to ensure that a
maximum amount of power is transferred from the solar panel to the
load (e.g., battery being charged). More specifically, it is known
that to deliver maximum power to a load, the power source
(including solar panels) should have the same internal impedance as
the impedance of the load. An MPPT module typically includes a
DC-to-DC voltage converter (VC) placed between the photovoltaic
(PV) array and the battery load. By converting the PV output
voltage to the battery voltage, the VC presents an ideal load to
the PV array allowing it to operate at its optimum voltage and
maximum power transfer. Generally, the DC-DC regulator (converter)
in MPPT charge controllers can be a boost, buck, buck-boost, SEPIC
or any other type of converter. The proper topology can be selected
based on the output voltage of solar panel and input voltage of the
load. Two of the most popular types of converters which have been
employed for MPPT are boost converter and buck converters.
[0005] Depending upon the relative magnitudes of the PV and battery
voltages, up to one-half of the generated power would be lost if a
voltage converter was not used. However, the MPPT module results in
a significant increase in the overall cost of a solar charging
system.
SUMMARY OF THE INVENTION
[0006] In one aspect of the invention, apparatus is provided for a
vehicle with an electric-start internal combustion engine. A DC
accessory bus is configured to connect to a plurality of electrical
accessories. A primary DC bus is adapted to connect to a main DC
battery and to an electric starter for the engine. A voltage
quality unit includes a voltage converter configured to convert a
voltage on the primary DC bus to a stabilized voltage on the DC
accessory bus during a starting operation of the electric starter.
The voltage quality unit includes bypass switches for connecting
the primary DC bus to the DC accessory bus when the electric
starter is not in the starting operation. A solar panel generates
an output voltage at a panel output. The bypass switches further
connect the voltage converter between the panel output and an
auxiliary load when the electric starter is not in the starting
operation. The voltage converter converts the solar panel output
voltage to an optimized voltage that optimizes power transfer to
the auxiliary load.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1 is a block diagram showing a typical vehicle
electrical system with a voltage quality module.
[0008] FIG. 2 is a voltage plot showing main battery voltage and
accessory bus voltage during an engine cranking event.
[0009] FIG. 3 is a schematic diagram of one embodiment of a
conventional DC- DC converter.
[0010] FIG. 4 is a block diagram showing one embodiment of a
vehicle having a solar power generating system.
[0011] FIG. 5 is a plot demonstrating the need for voltage
conversion to maximize power transfer from a solar panel to a
load.
[0012] FIG. 6 is a block diagram of one embodiment of a
conventional solar power generation system with power point
tracking.
[0013] FIG. 7 is a block diagram showing a first embodiment of the
invention wherein a voltage converter is shared between a voltage
stabilization/quality system and a solar power generating
system.
[0014] FIG. 8 is a block diagram showing a second embodiment of the
invention wherein a voltage converter is configured to operate as
either a boost converter or a buck converter.
[0015] FIG. 9 is a schematic diagram showing one preferred
embodiment of a voltage converter useful in the embodiment of FIG.
8.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0016] The present invention combines a voltage stabilizing system
(e.g., a voltage quality module, or VQM) with a solar power
generation system to better utilize hardware components in a
vehicle which has an electric-start internal combustion engine
(ICE). A voltage converter in a conventional VQM is only used for
short periods of time (e.g., during engine cranking) and is
otherwise idle. A voltage converter included in a maximum power
point tracker (MPPT) for solar panel is active for long periods of
time, even when the vehicle is parked and unattended. Even though
the input and output voltage levels and the dynamic control needs
for the DC- DC voltage converter of the VQM and the MPPT are
difference, the invention successfully configures a single
converter to satisfy both systems. The invention reduces the number
of components required for a solar panel equipped vehicle, improves
efficiency, decreases the overall weight of the two systems, and
reduces the overall cost and packaging complexity.
[0017] A voltage converter/stabilization circuit compatible with
the requirements for both subsystems can be arrived at in at least
two different ways. In one scenario, since typical designs of a VQM
function over certain voltage and current ranges, a solar panel
system can be arranged in such a way that it provides an output
matching these voltage and current ratings. In that case, the
voltage converter of the VQM can be used as a MPPT charge
controller without any modification. In a second scenario, the
circuitry and control strategy of a VQM can be designed to be
adaptable to different design architectures of the solar panel
system (e.g., settable to different voltages and currents), while
retaining its ability to perform across the required voltage and
current ranges during cranking.
[0018] Operation of a conventional voltage quality module will be
described with reference to FIGS. 1-3. A typical vehicle electrical
system in FIG. 1 includes a main battery 10 connected between
ground 11 and a primary DC bus 12. An alternator/generator 13
driven by an internal combustion engine (not shown) charges battery
10 during engine operation. An electric starter motor 14 is
selectably connected to main battery 10 by a relay switch 15 in
order to crank (i.e., start) the combustion engine. A master engine
control unit (ECU) 16 controls the state of switch 15 in response
to a manual ignition switch or a remote start signal, for
example.
[0019] ECU 16 is connected to a control section 20 in VQM 17 via a
multiplex bus (MUX) and by signal lines carrying Ignition status
and Crank status signals, for example. Primary DC bus 12 is
connected to an input of a voltage converter (VC) 21 and a bypass
relay switch 22. The outputs of VC 21 and bypass relay 22 are
connected to a DC accessory bus 18 that supplies a plurality of
electrical accessories 19, such as an audio system, cellular phone
system, navigation system, driver information/display system,
lighting devices, or other electronic devices. Control section 20
sets that state of bypass relay 22 and provides command signals to
control VC 21 based on whether an engine cranking event is
underway. When relay 22 is closed by control section 20 (e.g., a
vehicle ignition switch is in the On or Accessory position), then
VC 21 is deactivated and main battery 10 directly supplies the main
system voltage (e.g., 12 volts) to bus 18. During cranking, control
section 20 opens relay 22 and activates VC 21 using a variable duty
cycle that is dynamically controlled to continue to supply a
regulated voltage V.sub.reg (e.g., 12 volts) to bus 18.
[0020] FIG. 2 compares a main battery voltage trace 24 and a
voltage converter output voltage trace 30 during a cranking event.
An engine start signal is generated at an instant 25. The engine
starter motor is energized after a brief delay resulting in a
drop-off 26 in the voltage available at primary DC bus 12. During
the delay, VQM 17 transitions at 31 from the bypass mode to a boost
mode in order to begin to generate a stabilized voltage V.sub.reg
at 32 and relay 22 is opened. Eventually the power drain from the
starter motor decreases and the battery voltage on bus 12 recovers
at 27 until being fully recovered along line 28. Relay 22 can then
be closed and VC 21 is deactivated.
[0021] To provide boost conversion for VC 21, FIG. 3 shows an
example topology for a DC-DC converter 35 that receives a variable
DC voltage from the main battery at inputs 36 and provides
regulated voltage V.sub.reg at outputs 37. An inductor 38 stores
energy when a switch (e.g., MOSFET) 39 is ON and then transfers the
energy via a diode 40 to a capacitor 41 and resistor 42 when switch
39 is OFF. By modulating the duty cycle of switch 39 (e.g., using
voltage feedback in the control section) the amount of transferred
energy, and thus the output voltage, can be controlled.
[0022] Turning to a typical vehicle system for generating and
storing electrical energy using solar cells, FIG. 4 shows a vehicle
44 with a roof-mounted solar panel 45. A Maximum Power Point
Tracking (MPPT) charge controller 46 can be connected to recharge a
battery 47 (which can be the main vehicle battery, in which case it
might only be recharged when the vehicle is not in use) or
connected to auxiliary loads 48 (which can include an auxiliary
battery capable of being continuously recharged). Auxiliary loads
48 can include DC loads driven from DC power or can include a DC-AC
converter (i.e., an inverter) driving AC loads.
[0023] FIG. 5 shows a power transfer characteristic 50 for a
typical solar panel wherein the DC current flow from the panel is
plotted against the terminal voltage of the battery under charge.
In this example, the solar panel is rated at 17 Volts and 4.4 Amps
(i.e., a maximum power of 75 Watts). A curve 51 shows the actual
power transferred to a battery load for different battery voltages.
A peak power transfer occurs at point 55 where the battery load
voltage matches the nominal voltage of the solar panel (e.g., at
about 17 Volts in this example). If an unmodified solar panel
output was used to charge a typical automobile battery of 12 Volts
as shown at 52, then a high current is obtained from the solar
panel at 53 but a non-optimal power transfer shown at 54 is
obtained. A load voltage corresponding to point 55 would instead
deliver a maximum power to the load. Consequently, a DC-DC voltage
converter has been used in order to present an optimized load to
the solar panel while delivering the correct voltage to the load.
The voltage converter introduces its own internal losses, but these
are typically much less than the power lost without conversion. As
shown in FIG. 6, charge controller 46 preferably includes an MPPT
controller 46A and a DC-DC converter 46B. For a fixed load and
fixed solar panel configuration, MPPT controller 46A can also be
fixed (i.e., nonadaptive). In the event that the load voltage or
the solar panel configuration is variable, MPPT controller 46B can
use adaptive feedback. In a typical vehicle system, MPPT controller
46A may be fixed and the voltage may be stepped down from a higher
solar panel voltage to a lower battery voltage.
[0024] Since the boost converter (i.e., stabilization circuit) in a
VQM system is used only during cranking events of the vehicle
(usually only 5 seconds at a time) and considering similarities
between VQM and MPPT hardware (e.g., both use DC-DC converters),
the invention integrates these separate systems in order to share a
single voltage converter. This reduces the costs of adding solar
power generating capabilities to vehicles by decreasing the
packaging complexities of the system and decreasing the number of
added components.
[0025] FIG. 7 shows a first embodiment of an apparatus 50 for
combining voltage stabilization and solar power generation in a
motor vehicle with an electric-start internal combustion engine. A
main battery 51 powers a primary DC bus 52 to continuously
interface with an alternator/generator 53 and a starter motor 54. A
DC accessory bus 55 connects to a plurality of electrical
accessories 56 all configured to operate off of a nominal battery
voltage. Thus, proper operation of accessories 56 would be
disrupted during the natural voltage drop-off during a cranking
event if they only depended on main battery 51 for supplying
power.
[0026] Vehicle apparatus 50 includes an auxiliary battery 57 for
storing energy from solar power generation. Instead of or in
addition to battery 57, other DC loads (or AC loads with one of the
DC loads being a DC-AC inverter) can be supplied using the solar
power. A stabilization circuit 58 (e.g., a boost converter) has an
output selectably connected to either electrical accessories 56 or
auxiliary battery 57. A control section 60 is connected to
stabilization circuit 58 and to a control input 61 (e.g., a
magnetic solenoid) of a relay switch with controlled switching
elements 62, 63, and 64. Switching element 62 selectively connects
primary DC bus 52 to either electrical accessories 56 or an input
of stabilization circuit 58. Switching element 63 selectively
connects an output of stabilization circuit 58 to either electrical
accessories 55 or auxiliary battery 57. Switching element 64 is an
optional feature that can be used for selectively connecting solar
panel 65 and diode 66 to the input of stabilization circuit 58.
[0027] The embodiment in FIG. 7 is particularly adapted to use a
stabilization circuit 58 with a voltage converter which is
unmodified from a typical VQM system. More specifically, FIG. 7 is
adapted to operate stabilization circuit 58 as a boost converter.
In order to employ boost conversion, the output voltage of solar
panel 65 needs to be less than the stabilized voltage that is
provided to electrical accessories 56 during the cranking phase. In
addition, it is convenient if the nominal voltage of auxiliary
battery 57 is designed to be the same voltage (e.g., 12 Volts) so
that stabilization circuit 58 always regulates to the same target
voltage. Nevertheless, a different voltage could be used for the
auxiliary battery and target voltage for solar charging if desired.
Relay switching elements 62 and 63 have positions labeled 1 and 2.
In position 1 (when the engine starter motor is not in a starting
operation), a bypass state is obtained for the VQM function so that
stabilization circuit 58 is connected between solar panel 65 and
auxiliary battery 57 and primary DC bus 52 is connected to
electrical accessories 55. During a cranking event, bypass switch
elements 62 and 63 are in position 2 wherein stabilization circuit
58 is connected between primary DC bus 52 and accessory bus 55.
Thus, when the electric starter is in the starting operation,
energy from solar panel 65 is not utilized. When switching element
62 is in position 2, switching element 64 may be open in order to
isolate solar panel 65. However, switching element 64 may not be
necessary in some embodiments since diode 66 would usually be
either be reverse biased so that no current flows from solar panel
65 or any current flowing would be sufficiently small that it would
not be detrimental to system operation.
[0028] The constraint in this embodiment that the output voltage
from solar panel 65 has to be compatible with stabilization circuit
58 being a boost converter is easily satisfied by arranging solar
panel 65 to supply a voltage lower than the voltage needed by the
charging (auxiliary) load. For example, if the voltage of auxiliary
battery 57 is 12 V, the individual solar cells contained on a solar
panel can be interconnected to provide a voltage less than 12 V.
For example, in a solar panel containing 60 solar cells wherein
each cell has a nominal output voltage of 0.5 V, the cells could be
connected in various series and parallel branches to produce an
appropriate voltage. A layout with 3 branches connected in parallel
wherein each branch contains 20 solar cells results in a solar
panel with an output of 10 V. During solar charging, boost
converter 58 converts the 10 V solar panel output to an optimized
voltage of 12 V for transferring power to auxiliary battery 57.
[0029] A more generalized embodiment of the invention is shown in
FIG. 8 wherein it is not necessary for the voltage from the solar
panel to be smaller than the target charging voltage for the
auxiliary load (e.g., auxiliary battery, DC loads, or DC-AC voltage
converter with AC loads). In this case, additional relay switching
elements 67 are added as a double pole double throw (DPDT) relay
which reverses the power flow direction through stabilization
circuit 58 when connected between solar panel 65 and auxiliary
battery 57. A magnetic actuator 68 moves elements 67 between
positions 1 and 2 according to a control signal from control
section 60. Using reversal, stabilization circuit 58 can operate as
a boost converter during an engine starting operation in order to
stabilize the diminished main battery voltage and operate as a buck
converter when not in the starting operation in order to reduce an
output voltage from solar panel 65 to a lower voltage of auxiliary
battery 57. The embodiment in FIG. 8 can be programmable in order
to adapt a particular module design to work in systems having
different voltage levels (e.g., whether the solar panel voltage is
greater than or less than the voltage of the auxiliary load).
[0030] FIG. 9 provides a circuit topology for a DC-DC converter 70
with selective buck and boost operational modes for both directions
of power flow through the unit. An inductor 71 is connected in an
H-bridge configuration with switching devices (e.g., MOSFETs)
S1-S4. A left-side smoothing capacitor 72 and a right-side
smoothing capacitor 73 can each be either an input or an output of
converter 70 depending on a selected power flow 74 or 75.
[0031] With the voltage source (i.e., main battery or solar panel)
connected to the left side and the auxiliary load connected to the
right side of converter 70, gate switching signals can be provided
that turn S3 continuously ON, S4 continuously OFF, and modulate S1
and S2 OFF and ON to create a synchronous buck converter wherein
power flows from left to right. Alternatively, S1 can be switched
continuously ON, S2 continuously OFF, and S3 and S4 modulated OFF
and ON to obtain a synchronous boost converter also having power
flow from left to right.
[0032] With the voltage source (i.e., main battery or solar panel)
connected to the right side and the auxiliary load connected to the
left side of converter 70, gate switching signals can be provided
that turn S1 continuously ON, S2 continuously OFF, and modulate S3
and S4 OFF and ON to create a synchronous buck converter wherein
power flows from right to left. Alternatively, S3 can be switched
continuously ON, S4 continuously OFF, and S1 and S2 modulated OFF
and ON to obtain a synchronous boost converter also having power
flow from right to left.
* * * * *